1. Technical Field
The present invention relates to video processing and more particularly to a system and method for detecting objects in video.
2. Description of the Related Art
Background subtraction is a method for finding moving objects in a known background. An incoming image is compared pixel-by-pixel with a stored reference image and a difference mask is computed. Most such algorithms work on a very local basis. Neighboring pixels (in space and time) are considered only in a post-processing morphology stage. This can be a problem especially with shadow removal algorithms and may cause certain textured objects to be ignored. That is, it is possible for adjacent pixels to be corrected in opposite directions (e.g. one brightened, one dimmed) such that neither is perceived as different from the background pattern.
One solution to this dilemma is to not employ a pixel-based shadow removal algorithm, but instead detect all regions and use a post-processing method to determine if certain areas are shadows. This can be done by carefully looking for bounding edges around the object. Yet, this can be a time-consuming operation and the rules for when to break a shadow portion off a larger blob are difficult to formulate. Furthermore, in a highly textured environment (e.g. some outdoors scenes, or in a cluttered office) there is likely to be edge information near the boundary of a region no matter how the region was formed.
Another possible post-processing rule would be to search the interior of a region for texture and compare this to the texture found in the original background image. Once again, however, the criteria governing when to retain or dismiss a region are problematic.